I never encountered your set of problems before.  I had trouble initially with the card after a few light overlclocks: the card would not boot up, and windows would artifact then crash if I opened any app (even driver settings) that involved using the gpu. I realized after a few hours the problem was in my motherboard (H55n), I tweaked with bios and found the most stability with an overclocked PCI-E bus at 120 MHz, I have no idea why this is. Afterwards, I was not able to alter the gpu core or mem clock (only gpu voltage), even in drivers settings page, because the card was set at ULPS mode (according to Trixx), I did a clean windows install and all problems went away (last option on the table). But I will be getting a new motherboard and cpu soon, I am curious to know what is the cause for your computer not allowing you to change clock settings, I hope I don't run into the same issue on my new setup.

Oh man you will have a thrill on the waterblock. I am using the full card EK block, with the cold winter air outside I can reach 1300 MHz (+800 MH/z) on 1.1V at 32 degrees Celsius. Anything higher settings for the core results in artifacts and crashes (possible to reach 50% overclock with max overvolt on Trixx = 1375 MHz, but not feasible). I keep mine clocked conservatively at 1250 MHz (760-770 MH/z). Enjoy!

Yeah I was able to reach 825 MH/s on a full EK waterblock at about 1300 MHz core.  The voltage needs to be around +1.1V for stability, and artifacts begin to  appear significantly at that speed, anything higher than 1350 MHz crashes fast on 1.1V (1375 MHz = 50% overclock, crashes in an instant, unless doing max overvolt, but not feasible for many obvious reasons) on watercooling.  On air cooling artifacts appear around 1225 MHz (~70 C), watercooling around 1300 MHz (~32 C); temperature appears to be factor in this, but I won't get away with this for long since winter is ending, and no more freezing outside air will be chilling my 200mm radiator.

Without a doubt the 7990 will reach over 1 GH/s, but whether a 7990 could attain close to double the hashing rate of what I reach on my 7970 I would not be easily convinced, unless someone can accomplish it through trial (even if any modding is needed to be stable).  The major issues to consider is the amount of heat a single 7970 can produce just through its own vrm; one could speculate that a 7990 would draw close to 500 watts on a single board.  Thus the amount of electrical current needed is extremely high, and cooling would  probably be the top concern for an overclocked hashing 7990; besides when you begin to overclock, the current also rises up to a point, until which the voltage will need to be raised.  I am just wondering how a  significantly overclocked 7990 would stand on air cooling: temperature-wise, power consumption-wise, and then noise-wise.  I guess all we can do is wait and see how this upcoming video card performs once it is released.

Has anyone tried using SDK 2.5 on a 7970?

If you want to get a fairly quick understanding on electromigration and how atomic wire structure (chemical) changes as result of temperature and electrical current, there is a pdf document from some researchers on semiconductors at Arizona State University that is informative:

http://schroder.personal.asu.edu/Electromigration.pdf

In a nutshell:
Pretty neat that it mentions how hardware failure may take a very long time under "normal operating conditions," but is temperature dependent --> increasing temperature from 30 Celsius to 250 Celsius results in hardware lasting 30 seconds (example); in addition integrated circuits today use copper which does not electromigrate as fast as aluminum; the smaller the chip (40 nm, 32 nm, 28 nm, etc) the more prone it is to electromigration, because a higher amount of current is running through a thinner wire!

There is a post here that can demonstrate how to find out which SDK you have:

https://bitcointalk.org/index.php?topic=57784.0

Hmm that is interesting, I have used a 6850 to mine through bitminter and my hash rate did not change when I rigorously underclocked the graphics ram, but it did keep the card slightly cooler, which is probably a reason why many people might do this. On the other hand, it could be that some miners have optimizations for a specific version of the AMD app SDK that may improve hashing by utilizing graphics ram. Now I use a 7970 with these optimizations, but increasing or decreasing the graphics ram does not impact my hash rate. How long did you run your mining app to record those values in the graph (assuming no video or graphic demanding software was running simultaneously)?

The bios profile switch is located right beside the crossfire fingers, its very small; I was only able to lower my memory clocks after setting the switch to the second profile, I do not know if the same will happen to your card.  Other than the switching the bios profile I guess the remaining options might be drivers or driver settings, but it guess you might have already tried both.  Unless if you decide to flash the bios profile (2nd profile), and set your own values for the card's default core voltage, core frequency, and memory speed: this approach would be more effective than AB or other programs, I seen it done, yet I never attempted it, I'm sure others control power consumption better with this approach in their mining rigs. If I am not mistaken you need to capture your video bios, edit to alter its power/frequency profile settings (if not all of them), then use ATIflash; that is as much as I know.  I don't know if this helps, if not hopefully you find a solution that might not need re-installing an OS.

Have you by any chance tried using Sapphire Trixx to manipulate clocking and voltage? I never needed to alter any config files, and I never tried AB, but I can configure my 7970 rather well with catalyst (latest drivers) or Trixx even if both run simultaneously (changing the settings on one overrides the other and vice versa).  The only issue I have is not being able to get my ram lower than 1150 MHz (according to GPU-Z), but not a major issue. Did you change the physical BIOS profile switch on your card?

I encountered the exact same issue with the same cards, how did you fix it? I was under the impression the 7970 distributes its power over graphics-demanding applications, the more opened while mining, the lesser the hash rate; on the other hand my 6850 just ran choppy graphic programs without losing much hash rate.

I run a single 7970 with one full card EK waterblock. My mining operation is in the same room that I sleep; the benefit is the reduction in noise (200mm radiator, quiet pwm pump, and low fan speed), watercooling also allows you to overclock a card far more if energy cost is not an issue (I can reach over 800 MH/s on a single 7970 watercooled on 1275 MHz core, which draws 240 watts).

You need to find out the wattage of the graphics card (GPU-Z or multimeter) or the computer at the plug, then you divide your hash rate by watts, then you achieve MH/W.  Getting a graphics card that cheap to bitcoin mine may not be a bad idea, but do not forget computer hardware depreciates over time, so selling it in the future when it further depreciates may not be as profitable as investing into hardware that is more valuable and powerful as now.  This is just the line of thinking I follow in order to achieve the most profit over a period of time.

Has anyone been having issues with the rewards? I have mined for the past 5 days and have not received any btc or nmc in my account.

I just joined the forums, and I must say the new beta works far better than the previous version on my 7970; I reached only 680 MH/s before, now I can reach 833 MH/s on 1310 MHz core.

Like the others have already mentioned, this type of card just blows the hot air from the graphics card around your computer case. A reference designed 7970 with a blower fan is quite loud, but gets the job done in displacing the heat produced by the card. Another consideration (which I currently use) is to get a full card waterblock (universal blocks do not cool 7970 mosfets, so the board will crash in minutes at high clocks under load).

That cannot be right, such a number is too high for a single 7970. I can run mine at 1.31 GHz and achieve 833 MH/s.  In order to reach 1.34 GH/s either the card is clocked way over 2 GHz (doubtful) or there is more than one graphics card in the system.

I have not tried yet to lower the power consumption on my card, but I have it overclocked to 1275 MHz core, RAM is more difficult to modify with software, but using the new bitminter beta just released I can achieve 780 MH/s; GPU-Z sensors say my overall power consumption is 206.3 watts; so if my calculations are correct this is 3.78 MH/watt. This card is can far more, with the new AMD drivers I can pull 833 MH/s at 1310 MHz, but it will crash in a few seconds unless I raise the voltage.

The issue of trusting a bank differs from trusting bitcoin in many ways. The most obvious being government oversight in monitoring the "flow of money," needless to say there are established laws on how to regulate the flow of money in a financial system. Bitcoin lacks this sense of a "regulatory mechanism" and replaces it with us users. Whether this is good or bad I cannot tell, yet many people argue both ways.

I'm running a 7970 as well, I have not had any issues with running it 24/7. I keep my power plan on win 7 to High performance (I lower voltages on other components to lower power consumption in BIOS). I did not change any of the CPU BIOS settings other than disabling two out four cores. Is your 7970 the main display adapter or is it used as an "auxiliary adapter"?

My mining operation setup consists of just a 7970 (1275 MHz core) so far.  Since I sleep in the same and only room that my machine is running for 24/7, I water cool to increase the clock to a certain level of efficiency, and to keep the noise down to the point of absolute quietness.  Other than that, watercooling can be expensive unless planned carefully.

You could try using Sapphire Trixx, I managed to get 600 MHz RAM to run. Trixx may be more useful than Afterburner, but that is just the word on the street. Another approach could be to edit and reflash the BIOS on your video card, allowing you to run RAM at its idle status of 150MHz, while the core can be at a much higher setting.